Sliding members are used in various fields such as bearing member, various roll materials for rolling, vane for compressor, gas turbine blade, engine parts such as cam roller and so on. For such sliding members, a ceramic material that is lightweight and has high strength is increasingly used. In particular, a silicon nitride sintered compact is excellent in mechanical strength and abrasion resistance and therefore progressively applied to bearing members such as a bearing ball and so on.
For the bearing members such as the bearing ball and so on using the silicon nitride sintered compact, it has been proposed to improve the abrasion resistance and so on represented by the mechanical strength and rolling life, for example, based on control of the sintered compact composition (the kinds, the addition amounts and so on of sintering aids), control of forms of the aid components in the sintered compact, control of manufacturing process and so on (see Patent Reference 1 and 2). Patent Reference 1 describes a silicon nitride sintered compact improved in abrasion resistance by containing TiN grains having an average grain diameter of 0.1 μm or less. Patent Reference 2 describes a silicon nitride sintered compact containing at least one of TiN and TiCN as a Ti compound.
In electronic equipment having a disk medium such as an HDD, DVD or the like, its rotation shaft is rotated at a high speed by a rotation driving apparatus such as a spindle motor to work various disks mounted on the rotation shaft. It is tried that a bearing ball made of a silicon nitride sintered compact that is lightweight and has excellent abrasion resistance is applied to a bearing of the rotation shaft rotated at a high speed. However, conventional bearing balls made of silicon nitride sintered compact have a drawback of large variations in rolling life when used for a bearing of the rotation shaft rotated at a high speed, for example, such as 5000 rpm or more. Therefore, the bearing balls have not necessarily satisfied sufficient reliability and durability.
Patent Reference 1: JP-A 2004-002067 (KOKAI)
Patent Reference 2: JP-A 2006-036554 (KOKAI)